The present invention relates to an internal grinding machine, particularly to the means for feeding and discharging a workpiece thereof.
A prior art internal grinding machine such as shown in FIG. 7 comprises a lower roll 1 rotatably provided at a frame (not shown), an upper roll 2 provided rotatably at a frame above the lower roll 1 and movable further and closer in relation to the lower roll 1, the control axis of which is set slightly (h) horizontally off (to the left in the figure) the central axis of the lower roll 1, and a shoe 5 provided on a side opposite (on the right in the figure) to the side on which the off-set is provided between the lower roll 1 and the upper roll 2 (on the left in the figure), the end face of which contacts with and supports a workpiece 4 fed in a support space 3 between the upper and lower rolls 2 and 1. A workpiece 4 is supported in the support space 3 enclosed between the upper and lower rolls 2 and 1 and the shoe 5, and the internal surface 4a of the workpiece 4 is grounded by a rotating grinder (not shown).
When grinding of a workpiece is completed, an unfinished workpiece 4b is fed by a pusher 7 along a shoe 5 into the support space 3. At this moment, the finished workpiece 4 which is pushed by the unfinished workpiece 4b forces away an elastic holding-down rod 8 and is discharged outside of the machine (to the direction of the arrow) from the support space 3; and the unfinished workpiece 4b is held down by the elastic force of the holding-down rod 8 so that the unfinished workpiece 4b is not discharged together with the finished workpiece 4.
However, since a conventional internal grinding machine has a structure in which a workpiece is fed through the use of such workpiece charge means as described hereabove, there are chances that feeding and discharging of a workpiece are not properly carried out. A method of discharging a finished workpiece with the use of an elastic holding-down rod 8 operates well when diameter and width of a workpiece are sufficiently large. But on the other hand when they are very small, the holding-down rod 8 have to be very thin and consequently the adjustment becomes very difficult.
As shown in FIG. 8, it is difficult to keep a constant relation between a contact angle 8 and the length of a rod L. If the contact angle 8 is misadjusted as shown in FIG. 9, an unfinished workpiece sometimes sticks to the end face of the pusher 7 due to oil and returns with the pusher 7 without having been correctly discharged into the support space 3. If the rod length L is misadjusted as shown in FIG. 10, it happens that a finished workpiece is not discharged and trapped together with an unfinished workpiece, which disables correct discharge of workpiece one by one.